Pro-Palestinian and pro-Israel groups have clashed at the University of California, Los Angeles (UCLA) as demonstrations over the war in Gaza continue across US campuses.
Nationwide rallies - during which there have been hundreds of arrests - showed no sign of stopping over the weekend.
At UCLA "physical altercations broke out" after a barrier separating the two sides was breached, an official said.
The White House has insisted that demonstrations must remain peaceful.
National Security Council spokesman John Kirby told ABC that the US government respects the right of protesters demonstrating over the Israel-Gaza war.
But he condemned antisemitic incidents that have been reported, as well as "all the hate speech and the threats of violence out there".
At UCLA, a pro-Palestinian encampment has grown in size in recent days, as has a group of pro-Israeli counter-protesters.
The Israeli American Council (IAC) organised the counter-protest. It recently said it had "profound concern" over the antisemitism reported elsewhere, including at Columbia University in New York City.
Many pro-Palestinian protesters who spoke to the BBC there sought to distance themselves from antisemitic incidents. In some cases they have blamed outside agitators.
A group of 21 Democratic members of Congress has called on Columbia to end what they call the "unauthorized and impermissible encampment of anti-Israel, anti-Jewish activists on campus", in a letter obtained by Axios. Similar calls for action had largely come from the Republican side of the political divide.
In a fresh statement on Monday, Columbia head Dr Minouche Shafik said "alternative internal options to end this crisis" were under discussion, after talks between protest organisers and the university failed to result in a deal.
At least some of the protesters involved in the disturbances at UCLA appeared to have come from outside the university, the Reuters news agency reported.
The two groups remained peaceful until Sunday, when campus police with batons separated them as they pushed and shoved each other, and traded punches.
It was not immediately clear which group broke through the barrier between them.
"We are heartbroken about the violence that broke out," the university said, adding that additional security measures had been introduced.
Tensions flared at US universities after the 7 October Hamas attack, in which about 1,200 people were killed in Israel, and the retaliatory Israeli military assault that has killed more than 34,000 people in Gaza.
In the last fortnight, a nationwide uprising has emerged which university officials and law enforcement have struggled to contain. They have blamed outside groups for infiltrating the demos.
The movement seems to have been emboldened by the arrest of more than 100 protesters at Columbia after police were called to clear an encampment.
Hundreds of people have since been arrested in locations across the US - many of whom had pitched their own tents on university grounds.
The protests have also spread to Canada, with a pro-Palestinian camp of about 20 tents now installed in the grounds of Montreal's McGill University.
Activists in both countries are demanding a ceasefire in the conflict, and that their universities - many with massive endowments - cut their financial ties, or divest, from Israel.
They say that companies doing business in or with the nation of Israel are complicit in its ongoing war on Gaza - and so are institutions that invest in those companies.
Officials in the US have also scrambled to tackle alleged incidents of antisemitism, with a number of Jewish students voicing fears for their safety.
At several campuses, they have spoken of incidents ranging from chants and signs supporting Hamas - a proscribed terror group in the US - to physical altercations and perceived threats.
Northeastern University in Boston, Massachusetts, reported "virulent antisemitic slurs" in a statement on Saturday that accused "professional organisers with no affiliation to Northeastern" of infiltrating a student protest.
More than 100 people were detained, it added.
In other recent developments:
Among hundreds of other activists arrested over the weekend was Green Party presidential candidate Jill Stein, who was detained with dozens of others at Washington University in St Louis, Missouri. The university said they had been asked to leave "multiple times". Ms Stein told local media that the arrests were a "really bad look" for the institution
Protesters at Yale University set up a new encampment after a previous one was cleared by police, the student newspaper reported
California State Polytechnic University, Humboldt, has become the latest institution to request that students switch to virtual classes
More than a dozen students were arrested at University of Georgia, Athens, on Monday morning
